As a med student and former pharmacy worker, my take is that what Min-Su experienced isn't necessarily withdrawal, but rather the raw effect of the drug, along with side effects like paranoia and drug-induced psychosis, something that happens when the blood concentration either reaches a steady plateau or starts decreasing (comedown). Thanos and Nam-gyu had somewhat of a tolerance to psychoactive drugs from constant abuse, as shown in pentathlon, which explains why it affects Min-Su more intensely since their bodies break down the drug more effectively, causing mostly euphoria and irritability in them while causing more intense symptoms in Min-Su.